Class II malocclusion is highly prevalent in our society and there is considerable demand for its treatment. The most advantageous timing for such treatment is poorly understood. Two basic timing strategies are common: 1) correction is achieved in two separate phases, one during pre- adolescence and the other during the teen years. 2) The entire correction is accomplished in one phase of active treatment during the adolescent years. The short-term goals of this project are as follows: 1) to compare the efficacy, costs and benefits of the early phase of Class II correction with observation only during the same period; 2) to determine how efficacy, costs and benefits are modified by the initial severity of the Class II malocclusion; and 3) to determine if a retention plan alters the outcome in these cases. A secondary goal will be to compare efficacy, costs and benefits of two commonly used early treatment appliances (i.e. headgear and activator). The long-term objective of the study will be to make similar comparison between patients treated only at adolescence and those who experience an early intervention aimed at initiating a correction of their Class II malocclusion during pre-adolescence. Four hundred subjects (ages 8-9) with Class II malocclusions will be selected and grouped, based on severity, to receive either headgear, activator or observation; and retention or no retention. The progress of these treatments will be monitored longitudinally for differences and changes in craniofacial/dental morphology; functional status; damages to the dentition, psychosocial parameters (including compliance, motivation, satisfaction with and attitude toward treatment); and treatment time.